Stop in for a cup of coffee

I need to do the ceiling in mine. Walls have R21 with 1/2 plywood over it. Big issue is getting alot of stuff out to do it. Really just need a barrier up there. Want to use this.
https://www.insulation4less.com/ins...O0p2wbsuPPXcV9qhZ09tK_2bbGe1D5oBoCHXoQAvD_BwE